The present invention relates to a probe station adapted for low current and low voltage measurements in testing semiconductor wafers or other electronic devices. More particularly, the invention relates to a probe station with EMI shielding capabilities.
EMI, as used herein, means electromagnetic interference, while EMC means electromagnetic compatibility, i.e. a state of a device wherein the device is neither a source of nor influenced by EMI.
Such probe stations, as described for example in U.S. Pat. No. 6,492,822 to Cascade Microtech, Inc., usually comprise a housing wherein a chuck for supporting a substrate, e.g. a semiconductor wafer, is installed. The chuck may be fixed relative to the housing or be supported movably by means of a first positioning mechanism.
The housing has at least one aperture through which a first portion of the probe or probes extend in order to make contact to the substrate for testing purposes such that a first portion of the probe projects into the housing of the probe station. The probe itself is supported by a probe support which is arranged near the housing such that a second portion of the probe remains outside the housing of the probe station. The probe support may be fixed relative to the housing or be supported movably by means of a second positioning mechanism. Thus, either the chuck or the probe or both may be movable relative to the housing in the X and/or Y and/or Z directions. Additionally, the chuck or the probe or both may be rotatable relative to the housing about an axis, i.e. have a rotational degree of freedom.
In an alternative design of probe stations known in the art, the housing comprises a cap or a similar covering structure with EMI shielding properties which covers an opening in a top wall of the housing. In this case, the probe support is arranged near the covering structure of the housing and the apertures through which the probe or probes extend are provided in the covering structure.
The aperture or apertures are surrounded by an elastic gasket which can be made, for instance, of resilient foam. The foam must be electrically conductive for the gasket to have EMI shielding properties. In U.S. Pat. No. 6,492,822, the gasket is a sheet of such foam with a vertical slit which is self-closing, thus purportedly surrounding the probe snugly when it is inserted.
However, it has been found that, due to the lateral spreading of the slit by the probe permeating it, slot antennas which jeopardize effective EMI shielding may form around the probe. Moreover, movements of the probe in the X and Y directions are prevented while movements in the Z direction, i.e. vertical movements, are at least impeded due to the friction between the slit and the probe.
In US 2003/0038622 A1 (Peters et al.), a probe station is disclosed wherein the environment, i.e. the surrounding area, of the chuck is shielded from EMI by means of an electrically conductive flexible wall assembly containing flexibly extensible and retractable pleated wall elements. The wall elements are arranged in a manner which allows for a free movement of the chuck in X and Y directions. The assembly is mechanically complex and, therefore, expensive. Furthermore, the proposed solution holds a danger of slot antennas forming in the proximity of the edges of the wall elements.
It is, therefore, an object of the present invention to describe a probe station which overcomes the above mentioned drawbacks of the prior art. In particular, it is an object of the invention to provide a probe station which allows for effective EMI shielding of the passage between the probe support and the housing of such probe station through which the probe extends. It is another object of the invention to provide a probe station wherein the probe is entirely encapsulated in EMI shielding structures in order to improve the electromagnetic compatibility of the probe station. It is yet another object of the invention to disclose a probe station wherein the probe is freely movable in the X, Y and Z directions.